KABUL, Afghanistan (AP) — U.S. Army Staff Sgt. Robert Bales was charged on Friday with 17 counts of premeditated murder, a capital offense that could lead to the death penalty in the massacre of Afghan civilians, the U.S. military said.

The 38-year-old soldier is accused of walking off a U.S. military base with his 9mm pistol and M-4 rifle, which was outfitted with a grenade launcher, before dawn on March 11, killing nine Afghan children and eight adults and burning some of the bodies. It was the worst allegation of civilian killings by an American and has severely strained U.S.-Afghan ties at a critical time in the decade-old war.

It’s unclear what prompted the killings, but the case has drawn new attention to the debate over mental health care for the troops, who have experienced record suicide rates and high incidences of post-traumatic stress and brain injuries during repeated deployments in Iraq and Afghanistan.

Six other Afghans – a man, a woman and four children – were wounded in Panjwai district of Kandahar province, the spiritual birthplace of the Taliban. Bales also was charged with six counts of attempted murder and six counts of assault in those cases, according to Col. Gary Kolb, a spokesman for U.S. forces in Afghanistan who disclosed information from the charging document.

Bales, a father of two from Lake Tapps, Washington, was officially informed of the 29 charges just before noon local time at the U.S. military prison at Fort Leavenworth, Kansas, where he is confined.

His civilian attorney, John Henry Browne, said Friday that he believes the government will have a hard time proving its case and that his client’s mental state will be an important issue. Bales was on his fourth tour of duty, having served three tours in Iraq, where he suffered head and foot injuries.

The decision to charge him with premeditated murder suggests that prosecutors plan to argue that he consciously conceived the killings. A military legal official for U.S. forces in Afghanistan who spoke on condition of anonymity to discuss the case, noted that premeditated murder is not something that has to have been contemplated for a long time.

The maximum punishment for a premeditated murder conviction is death, dishonorable discharge from the armed forces, reduction to the lowest enlisted grade and total forfeiture of pay and allowances, Kolb said. The mandatory minimum sentence is life imprisonment with the chance of parole.

Legal experts have said the death penalty would be unlikely in the case. The military hasn’t executed a service member since 1961 when an Army ammunition handler was hanged for raping an 11-year-old girl in Austria. None of the six men currently on death row at Fort Leavenworth was convicted for atrocities against foreign civilians.

The charging document did not provide details about the killings, leaving the timeline unclear. The dead bodies were found in Balandi and Alkozai villages – one north and one south of the base.

Members of the Afghan delegation investigating the killings said one Afghan guard working from midnight to 2 a.m. saw a U.S. soldier return to the base around 1:30 a.m. Another Afghan soldier who replaced the first and worked until 4 a.m. said he saw a U.S. soldier leaving the base at 2:30 a.m. It’s unknown whether the Afghan guards saw the same U.S. soldier. If the gunman acted alone, information from the Afghan guards would suggest that he returned to base in between the shooting sprees.

It also is not known whether the suspect used grenades, Kolb said. The grenade launcher attachment is added to the standard issue M-4 rifle for some soldiers but not all, he said. Bales was assigned to provide force protection at the base.

The pre-dawn shooting spree has further frayed ties between U.S. troops and President Hamid Karzai as the two nations are negotiating agreements for America’s military footprint in Afghanistan after most international combat forces withdraw by the end of 2014. After the shootings, Karzai reiterated his demand that foreign troops leave posts near Afghan villages and pull back to larger bases.

The killings also have fueled anti-American sentiment in a country where violent protests raged for nearly a week last month after Muslim holy books and other Islamic texts ended up in a garbage burn pit at a U.S. base.

“By the laws of Islam, the soldier should be hanged,” Dost Mohammad, a shopkeeper in Kandahar, the provincial capital, said Friday. “While other countries’ laws say that this individual should be given a life sentence, from our point of view and that of other Muslims, this guy should be hanged.”

Afghan officials and villagers maintain that 16 civilians were killed. The U.S. military never announced a death toll, but said Friday that investigators had collected enough evidence to charge Bales with killing 17 civilians.

U.S. officials are working with Afghan officials to compensate relatives of the victims, money that likely would be disbursed to the eldest male of the family. Eleven of those who died were from one family.

Bales’ lawyer, who is based in the state of Washington, has said that his client remembers very little or nothing from the time the military believes he went on the rampage.

Browne told CBS’ “This Morning” on Friday that his client’s memory problems predate the shooting spree. Browne said Bales had earlier suffered a “serious” concussion that was not treated “for a variety of reasons,” which Browne did not explain.

Browne said he thinks the U.S. government will have difficulty proving its case against Bales because “there is no crime scene” and a lack of important physical evidence like fingerprints.

Two military defense attorneys also have been assigned to his case.

Browne has said that he wants to visit Afghanistan.

U.S. military officials said they would do what they can to protect Bales’ legal team in the event of such a visit but warned the shootings have heightened tension between U.S. troops and villagers in the area, and decisions about where the legal team could safely travel would have to be on a case-by-case basis at the time of any visit.

The charges launch what is likely to be a lengthy legal process.

Bales was assigned to the 2nd Battalion, 3rd Infantry Regiment of the 3rd Stryker Brigade Combat Team, of the 2nd Infantry Division, which is based at Joint Base Lewis-McChord in Washington. The U.S. Forces-Afghanistan has sent the charges to a special court-martial convening authority, the 17th Fires Brigade, an artillery unit based in Fort Lewis, Washington.

Lewis-McChord spokesman Lt. Col. Gary Dangerfield said Friday that officials at that base will have the legal responsibility of trying and managing the case against Bales, but it was not clear where the proceedings will actually take place, noting that Fort Leavenworth has the most updated security.

The commanding officer of that brigade has several options ranging from taking no action to ordering an Article 32 investigation, which is comparable to a preliminary hearing or grand jury process in U.S. civilian courts.

During the investigation, the defense will have an opportunity to see evidence and cross-examine government witnesses. An investigating officer will issue a report at the end of the probe in which he can recommend a court-martial; and add, delete or modify the charges. A mental assessment for Bales also is expected to be ordered.

He could be charged with other offenses later, according to the legal official. On Friday, a senior U.S. defense official said Bales was drinking in the hours before the attack on Afghan villagers, violating a U.S. military order banning alcohol in war zones.